Treatment of an aqueous waste stream from a hydrocarbon conversion process



Oct. 27, 1970 P. URBAN ETAL 3,536,618

TREATMENT OF AN AQUEOUS WASTE STREAM FROM A HYDROCARBON CONVERSION PROCESS Filed Sept. 16, 1968 V Q a K g, 1 $2 E s \a 2 g T Q. gm 8 '3 g-E Q s Q 00 i 0 g: Q E N g g "b b (n S 6; f \E a g a i a R1 Q g Q t N 3 3 E E 2 N wB [a g5 gig s 3) 1 $2 a Q x k ma a D Q q E a: m B Q) g 1 s k k /N VE/VTORS:

Peter Urban By Robert H. Rosenwa/d 1 ATTORNEYS United States Patent O 3,536,618 TREATMENT OF AN AQUEOUS WASTE STREAM FROM A HYDROCARBON CONVERSION PROCESS Peter Urban, Northbrook, and Robert H. Rosenwald,

Western Springs, 11]., assignors to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware Filed Sept. 16, 1968, Ser. No. 760,045 Int. Cl. C02c /04 US. Cl. 210-50 12 Claims ABSTRACT OF THE DISCLOSURE An aqueous waste stream containing NH HS, which is produced in a process for converting a hydrocarbon charge stock containing sulfurous and nitrogenous contaminants, is treated to produce elemental sulfur, NH and a treated aqueous stream suitable for recycle to the water-contacting step of the hydrocarbon conversion process, by the steps of: (a) catalytically treating the aqueous waste streams with oxygen at oxidizing conditions effective to produce an effluent stream containing NH OH, (NH S O and elemental sulfur or ammonium polysulfide; (b) separating sulfur and ammonia from the effluent stream from step (a) to form an aqueous stream containing (NH S O (c) subjecting the aqueous stream from step (b) and a sulfide-containing stream to reduction conditions effective to produce an aqueous efiluent stream containing a minor amount of ammonium polysulfide; (d) subjecting the effluent stream from step (c) to polysulfide decomposition conditions effective to produce an overhead stream containing NH H 8, and H 0, and an aqueous bottom stream containing elemental sulfur; (e) separating sulfur from the bottom stream produced in step (d) to form an aqueous stream which is suitable for recycling to the water contacting step of the process. Key feature of the treatment method is the use of a sulfide-containing stream in a reduction step to enable the continuous recycle of the treated water back to the water-contacting step of the hydrocarbon conversion process with consequential abatement of water pollution problems and substantial reduction of requirements for make-up water for the hydrocarbon conversion process.

The subject of the present invention is an improved waste water treatment method which finds utility in combination with a hydrocarbon conversion process where a charge stock containing sulfurous and nitrogenous contaminants is catalytically converted with cotinuous recovery of at least a portion of the sulfur and ammonia from the products of the hydrocarbon conversion reaction, and where it is desired to operate without causing any substantial water pollution problems. More precisely, the present invention relates to a process for the conversion of a hydrocarbon charge stock containing sulfurous and nitrogenous contaminants wherein a aqueous waste stream cotaining NH HS is produced by contacting the efiluent from the conversion step with a water stream, and wherein this waste stream is treated by the method of the present invention to recover elemental sulfur and ammonia and to produce a treated water stream which is suitable for direct recycle to the water contacting step of the hydrocarbon conversion process in order to remove additional quantities of NH and H 8 therefrom. The principal advantage of this improved method is that it enables the continuous direct recycle of the treated aqueous stream to the water-contacting step with consequential abatement of a substantial water pollution problem which heretofore has attended operation of these hydrocarbon conversion processes. A corollary advantage is 3,536,618 Patented Oct. 27, 1970 ICC the minimization of water requirements for the operation of this type of hydrocarbon conversion process.

The concept of the present invention developed from our efforts directed towards a solution of a substantial water pollution problem that is caused when a water stream is used to remove ammonium hydrosulfide salts from the effluent equipment train associated with such hydrocarbon conversion processes as hydrorefining, hydrocracking, etc., wherein ammonia and hydrogen sulfide side products are produced. The original purpose for injecting the water stream into the efiluent train of heat transfer equipment associated with these processes was to remove these detrimental salts which could clog-up the equipment. The waste water stream so-formed presented a substantial pollution hazard insofar as it contains sulfide salts which have a substantial biological oxygen de mand and ammonia which is a nutrient that leads to excessive growth of stream vegetation. One solution used commonly in the prior art to control this pollution problem is to strip NH and H 5 from this waste water stream with resulting recycle of the stripped water to the effluent equipment. Another solution is to sufficiently dilute the waste water stream so that the concentration of sulfide salts is reduced to a level wherein it is relatively innocuous and to discharge the diluted stream into a suitable sewer. Our approach to the solution to this problem has been directed towards a waste water treatment method which would allow recovery of the commercially valuable elemental sulfur and ammonia directly from this waste water solution by a controlled oxidation method. However, despite careful and exhaustive investigations of alternative methods for direct oxidation of the sulfide salts contained in this waste water stream, we have determined that an inevitable side product of the oxidation step appears to be ammonium thiosulfate. The presence of ammonium thiosulfate in the treated aqueous stream presents a substantial problem because for efficient control of the water pollution problem and in order to have minimum requirement for make-up water, it is desired to operate the waste water treating plant with a closed water loop. That is, it is desired to continuously recycle the treated water stream back to the water-contacting step of the hydrocarbon conversion process in order to remove additional quantities of the detrimental sulfide salts. The presence of ammonium thiosulfate in this treated aqueous stream prevents the direct recycling of this stream back to the water-contacting step primarily because the ammonium thiosulfate reacts with hydrogen sulfide contained in the effluent stream from the process to produce elemental sulfur, with resulting contamination of the hydrocarbon product stream with free sulfur which causes severe corrosion problems in the downstream equipment. In addition, ammonium thiosulfate is nonvolatile and will contribute to salt formation in the effluent equipment.

We have now found a convenient and simple procedure for removing the ammonium thiosulfate salts from the treated aqueous stream recovered from the controlled oxidation step to enable the preparation of an aqueous recycle stream which is suitable for direct passage back to the water-contacting step of the hydrocarbon conversion process. In other words, we have found that the problem caused by the presence of ammonium thiosulfate in the aqueous efiluent stream from the oxygen treatment step is effectively and efliciently solved by combining the oxygen treatment step, 'with a reduction step where H 8 or ammonium sulfide is utilized to reduce the ammonium thiosulfate with consequential formation of an eflluent stream containing ammonium polysulfide. The ammonium polysulfide can then be easily decomposed to enable the recovery of a treated water stream which is substantially free of thiosulfate and thus suitable for recycle to the water-contacting step of the hydrocarbon conversion process. One advantage associated with the procedure is the increased yield of elemental sulfur enabled thereby. Another advantage is the use of a readily available and inexpensive reducing agent. Yet another advantage is the fact that the reduction step does not require a catalyst. Still another advantage is the relatively mild conditions required for the reduction step.

It is, accordingly, an object of the present invention to provide an improved treating method which operates on an aqueous waste stream containing NH HS, which is produced in a hydrocarbon conversion process, to recover elemental sulfur, NH and a treated waste stream suitable for direct recycle to the water-contacting step of the hydrocarbon conversion process. A second object is to eliminate one source of waste water streams that can cause pollution problems in the vicinity of petroleum refineries. A third object is to substantially reduce the requirements for fresh Water or make-up water for the operation of a hydrocarbon conversion process wherein hydrogen sulfide and ammonia are produced as side products. A fourth object is to treat an NH HS-containing Waste Water stream, which is recovered from a watercontaining step of a hydrocarbon conversion process, in order to allow recycle of the water present in this stream directly to the water-containing step without contaminating the hydrocarbon product stream recovered from this process with elemental sulfur. Another object is to provide an improved treating method which operates on a waste water stream from a hydrocarbon conversion plant containing NH HS in order to recover sulfur and ammonia and to produce a treated aqueous stream which is substantially free of nonvolatile salts so that the treated aqueous stream can be injected ahead of the heat exchange equipment utilized in the plant to condense the effluent stream from the hydrocarbon conversion step associated therewith. Still another object is to provide a waste water treating method for the waste water stream recovered from hydrocarbon conversion processes such as hydrorefining and hydrocracking which method produces a treated water stream which can be continuously recycled to the hydrocarbon conversion process that is, to enable operation in a closed loop fashion with regard to the water stream utilized.

In one embodiment, the present invention relates to an improved method of treating an aqueous waste stream containing NH HS to produce elemental sulfur, NH and a treated aqueous stream suitable for recycle to a hydrocarbon conversion process. This aqueous waste stream is produced in a process for converting a hydrocarbon charge stock containing sulfurous and nitrogenous contaminants wherein this charge stock is subjected to a conversion step resulting in the formation of an efiluent stream containing substantially sulfur-free and nitrogenfree hydrocarbons NH and H 8. In this process, this effluent stream is contacted with a water stream and the resulting mixture cooled and separated to produce the aqueous Waste stream containing NH HS. The first step of the improved treating method of the present invention involves catalytically treating the aqueous waste stream with oxygen at oxidizing conditions effective to produce an efliuent stream containing NH OH, (NH S O and elemental sulfur or ammonium polysulfide. Sulfur and ammonia are, in the second step, separated from the efiiuent stream from the first step to produce an aqueous stream containing (NH S O The third step involves subjecting the aqueous stream from the second step and a sulfide-containing stream to reduction conditions effective to form an effiuent stream containing a minor amount of ammonium polysulfide. In the fourth step, the efiiuent stream from the third step is subjected to polysulfide decomposition conditions effective to produce an overhead stream containing NH H 5, and H 0 and a bottom stream containing elemental sulfur. Thereafter, in the fifth step, sulfur is separated form the bottom stream to form a substantially thiosulfate-free and elemental sulfur-free aqueous recycle stream. And, the final step involves recycling the aqueous recycle stream to the water-contacting step of the hydrocarbon conversion process.

In a second embodiment, the improved method of the present invention encompasses a method as outlined above in the first embodiment wherein the first step comprises contacting the aqueous waste stream and oxygen with a phthalocyanine catalyst at oxidizing conditions effective to produce an efliuent stream containing NH OH, (NH S O and elemental sulfur or ammonium polysulfide.

In a third embodiment, the present invention comprises the improved method outlined above in the first embodiment wherein the reduction conditions utilized in the third step include a temperature of about 200 to about 700 F., a pressure sufficient to maintain a part of the aqueous stream in the liquid phase and a contact time of about 0.01 to about 2 hours.

In a fourth embodiment, the present invention comprises the improved treating method as described in the first embodiment wherein a water-immiscible sulfur solvent is also charged to the first step and wherein the second step comprises: separating the efiiuent stream from the first step into a sulfur solvent phase containing sulfur and an aqueous phase containing NH OH and (NH S O and stripping at least a portion of the ammonia from this aqueous phase to produce an aqueous stream containing (NH S O In a preferred embodiment, the present invention comprises an improved method of treating an aqueous waste stream containing NHJ-IS which is produced in a hydro carbon conversion process where a hydrocarbon charge stock containing sulfurous and nitrogenous contaminants is subjected to a conversion step resulting in the formation of an effluent stream containing hydrocarbons, NH H 8 and where this efiiuent stream is contacted with a Water stream and the resulting mixture cooled and separated to form the aqueous waste stream. The first step of this improved method of treating this aqueous waste stream involves contacting a first portion of the aqueous waste stream and an amount of oxygen suflicient to provide a mole ratio of oxygen to NH HS of less than 0.5 :1 with a phthalocyanine catalyst at oxidizing conditions selected to produce an effluent stream containing ammonium polysulfide NH OH, and (NH S O The second step comprises subjecting the effluent stream formed in the first step to polysulfide decomposition conditions effective to produce a first overhead stream containing NH H S and H 0, and an aqueous bottom stream containing elemental sulfur and (NH S O In the third step, sulfur is separated from the bottom stream produced in the second step to form an aqueous stream containing (NH S O In the fourth step, the aqueous stream from the third step and a second portion of the aqueous waste stream are subjected to reduction condi tions, including a temperature of about 325 to about 400 F. and a pressure of about 100 to about 5000 p.s.i.g., and a contact time of about 0.05 to about 0.2 hours, to form an aqueous efiiuent stream containing a minor amount of ammonium polysulfide. In the fifth step, the effluent stream from the fourth step is subjected to polysulfide decomposition conditions to produce a second overhead stream containing NH H 8 and H 0, and an aqueous bottom containing elemental sulfur. Sulfur is then separated from the bottom stream from the fifth step to form an aqueous recycle stream which is substantially free of both ammonium thiosulfate and elemental sulfur. And, the final step involves recycling the aqueous recycle stream to the water contacting step of the hydrocarbon conversion process.

Other objects and embodiments are hereinafter disclosed in the following discussion of the input streams,

the output streams and the mechanics associated with each of the essential steps of the present invention.

As indicated above, the improved method of the present invention is principally utilized in combination with a hydrocarbon conversion process involving the catalytic conversion of a hydrocarbon charge stock containing sulfurous and nitrogenous contaminants. In particular, the waste water treating method can be utilized in conjunction with catalytic petroleum processes which utilize hydrogen in the presence of a hydrocarbon conversion catalyst to react with sulfur and nitrogen compounds contained in the charge stock to produce, inter alia, H 8, and NH Generally, in these processes, the hydrocarbon charge stock containing the sulfurous and nitrogenous contaminants and hydrogen are passed into contact with a hydrocarbon conversion catalyst comprising a metallic component selected from the metals and compounds of the metals of Group VI(b) and Group VIII combined with a refractory inorganic oxide carrier material at conversion conditions, including an elevated temperature and superatmospheric pressure, sufiicient to produce an effluent stream containing substantially sulfur-free and nitrogen-free hydrocarbons, hydrogen, H S, and NH One example of a preferred conversion process is the process known in that art as hydrorefining, or hydrodesulfurization. The principal purposes of a hydrorefining process is to desulfurize a hydrocarbon charge stock charged thereto by a mild treatment with hydrogen which generally is selective enough to saturate olefinic-type hydrocarbons and to rupture carbon-nitrogen and carbon-sulfur bonds but is not severe enough to saturate aromatics. The charge to the hydrorefining process is typically a charge stock boiling in the range of about 100 F. to about 650 R, such as a gasoline boiling range charge stock or a kerosine boiling range charge stock or a heavy naphtha, which charge stock contains minor amounts of sulfurous and nitrogenous contaminants which are to be removed Without causing any substantial amount of cracking or hydrocracking. The hydrorefining catalyst utilized is preferably disposed as a fixed bed in the conversion zone and typically comprises a metallic component selected from the transition metals and compounds of the transition metals of the Periodic Table. In particular, a preferred hydrorefining catalyst comprises an oxide or sulfide of a Group VIII metal, expecially an iron group metal, mixed with an oxide or sulfide of a Group VI(b) metal, especially molybdenum or tungsten. These metallic components are preferably combined with a carrier material which generally is characterized as a refractory inorganic oxide such as alumina, silica, zirconia, titania, etc. Mixtures of these refractory inorganic oxides are generally also utilized, especially mixtures of alumina and silica. Moreover. the carrier materials may be synthetically prepared or naturally occurring materials such as clays, bauxite, etc. Preferably, the carrier material is not made highly acidic. A preferred hydrorefining catalyst comprises cobalt oxide or sulfide and molybdenum oxide or sulfide combined with an alumina carrier material containing a minor amount of silica. Suitable conditions utilized in the hydrocarbon conversion step of the hydrorefining process are: a temperature in the range of about 700 to about 900 F., a pressure of about 100 to about 3000 p.s.i.g., a liquid hourly space velocity of about 1 to about 20 hr." and a hydrogen to oil ratio of about 500:1 to about l0,000:1 standard cubic feet of hydrogen per barrel of charge stock.

Another example of the type of conversion process with which the improved waste water treating process disclosed herein is preferably utilized is a hydrocracking process. The principal objective of this type of process is not only to effect hydrogenation of the charge stock but also to effect selective cracking or hydrocracking. In general, the hydrocarbon charge stock is a stock boiling above the gasoline range such as straight-run gas oil fractions, lubricating oil, cocker gas oils, cycle oils, slurry oils, heavy recycle stock crude petroleum oils, reduced and/or topped crude oils, etc. Furthermore, these hydrocarbon charge stocks contain minor amounts of sulfurous and nitroge nous contaminants which may range from about p.p.rn. sulfur to 3 or 4 wt. percent sulfur or more; typically, the nitrogen concentration in this charge stock will be substantially less than the sulfur concentrations except for some rare charge stocks, such as those derived from some types of shale oil, which contain more nitrogen than sulfur. The hydrocracking catalyst utilized typically comprises a metallic component selected from the metals and compounds of metals of Group VI(b) and Group VIII combined with a refractory inorganic oxide. Particularly preferred metallic components comprise the oxides or sulfides of molybdenum and tungsten from Group VI(b) and of iron, cobalt, nickel, platinum and palladium from Group VIII. The preferred refractory inorganic oxide carrier material is a composite of alumina and silica, although any of the refractory inorganic oxides mentioned hereinbefore may be utilized as a carrier material if desired. Since it is desired that the catalyst possess a cracking function, the acid activity of these carrier materials may be further enhanced by the incorporation of small amounts of acidic materials such as fluorine and/or chlorine. In addition, in some cases it is advantageous to include within the carrier material a crystalline aluminosilicate either in the hydrogen form or in a rare earth exchanged form. Preferred aluminosilicates are the Type X and Type Y form of faujasite, although any other suitable aluminosilicate either naturally occurring or synthetically prepared may be utilized if desired. Conditions typically utilized in the hydrocarbon conversion step of a hydrocracking process include: a temperature of about 500 to about 1000 F., a pressure in the range of about 300 to about 5000 p.s.i.g., a liquid hourly space velocity of about 0.5 to about 15.0 hr." and a hydrogen to oil ratio of about l000:1 to about 20,000:1 standard cubic feet of hydrogen per barrel of oil.

Regardless of the details concerning the exact nature of the hydrocarbon conversion step of these conversion processes, the effluent stream recovered therefrom typically contains substantially sulfur-free and nitrogen-free hydrocarbons, hydrogen, NI-I and H 8. In all of the conversion processes with which the present invention can be combined, it is an essential feature that this efiluent stream is admixed with a water stream, in a water-contacting step, prior to any substantial cooling of this effluent stream. Thereafter, the resulting mixture of water, hydrocarbons, NH and H S is cooled in any suitable cooling means, and then separated, in any suitable separating means, into a hydrogen-rich gaseous stream, a hydrocarbon-rich liquid product stream, and a waste water stream containing NH HS. As discussed previously, the uniform practice of the prior art has been to inject sufiicent water into the effiuent stream from the hydrocarbon conversion step upstream of the heat exchange equipment in order to wash out ammonium sulfide salts that would be otherwise produced when the efiiuent is cooled to temperatures below about 200 F. as indicated hereinbefore, an essential feature of the present invention is that the source of a major portion of the Water necessary to wash out these ammonium sulfide salts is a recycle aqueous stream produced by the improved treating method of the present invention. During start-up of the process of the present invention, and during the course of the process, additional make-up water may be added to the Water stream charged to the water-contacting step if desired. The total amount of water utilized is obviously a pronounced function of the amount of NH and H S in this effiuent stream; typically it is about 1 to about 20 or more gallons of water per 100 gallons of oil charged to the hydrocarbon conversion step. The resulting cooled mixture of the water stream and the efiluent stream is typically passed to a separating zone wherein it separates into a hydrogen-rich gaseous phase, a hydrocarbon-rich liquid phase and a waste water phase. The hydrogen-rich gaseous phase is then Withdrawn from this zone, and a portion of it typically recycled to the hydrocarbon conversion step through suitable compression means. The hydrocarbon-rich liquid product phase is typically withdrawn and passed to a suitable product recovery system which generally, for the type of hydrocarbon conversion processes within the scope of the present invention, comprises a suitable train of fractionating equipment designed to separate this hydrocarbon-rich product stream into a series of desired products, some of which may be recycled. The aqueous phase formed in the separating zone is typically withdrawn to form an aqueous waste stream containing ammonium hydrosulfide (NH HS) which is the principal input stream to the improved treating method of the present invention. This waste stream may, in some cases, contain excess amounts of NH relative to the amounts of H 3 adsorbed therein, but very rarely will contain more H 8 than NH because of the relatively low solubility of H 8 in an aqueous solution containing a ratio of dissolved H S to dissolved NH greater than about 1:1.

The amount of NH HS contained in this waste stream may vary over a wide range up to the solubility limit of the sulfide salt in water. Typically, the amount of NH HS is about 1.0 to about 10.0 wt. percent or more of the waste stream. For example, a typical waster water stream from a hydrocracking plant contains 3.7 wt. percent NH HS.

Following this separation step, the aqueous waste stream produced therein is passed to a treating step, the first step of the method of the present invention, wherein it is catalytically treated with oxygen at oxidizing conditions selected to produce an aqueous effiuent stream containing NH OH, (NHQ S O and elemental sulfur or ammonium polysulfide. In some cases, it is advantageous to remove dissolved or entrained oil contained in this waste stream by any suitable scrubbing operation prior to passing it to the treatment step; however, in most cases this waste stream is charged directly to the treating step.

The catalyst utilized in the treating step is a suitable solid oxidizing catalyst that is capable of effecting substantially complete conversion of the ammonium hydrosulfide salt contained in this waste stream. Two particularly preferred classes of catalyst for this step are metallic sulfides, particularly iron group metallic sulfides, and metal phthalocyanines. The metallic sulfide catalyst is selected from the group consisting of sulfides of nickel, cobalt, and iron, with nickel being especially preferred. Although it is possible to perform this step with a slurry of the metallic sulfide, it is preferred that the metallic sulfide be compounded with a suitable carrier material. Examples of suitable carrier materials are: charcoal, such as wood charcoal, bone charcoal, etc. which may or may not be activated prior to use; refractory inorganic oxides such as alumina, silica, zirconia, kieselghur, bauxite, etc.; activated carbons and other natural or synthetic highly porous inorganic carrier materials. The preferred carrier materials are alumina and activated charcoal or carbon and thus a preferred catalyst is nickel sulfide combined with alumina or activated carbon in an amount sufficient to provide about 1. to about wt. percent nickel as nickel sulfide.

Another preferred catalyst for use in this treatment step is a metal phthalocyanine catalyst combined with a suitable carrier material. Particularly preferred metal phthalocyanine compounds include those of cobalt and vanadium. Other metal phthalocyanine compounds that may be used include those of iron, nickel, copper, molybdenum, manganese, tungsten, and the like. Moreover, any suitable derivative of the metal phthalocyanine may be employed including the sulfonated derivatives and the carboxylated derivatives. Any of the carrier materials previously mentioned in connection with the metallic sulfide catalyst can be utilized with the phthalocyanine catalyst; however, the preferred carrier material is activated carbon. Hence, a particularly preferred catalyst for use in the treatment step comprises a cobalt or vanadium phthalocyanine sulfonate combined with an activated carbon carrier material. Additional details as to alternative carrier materials, methods of preparation, and the preferred amounts of catalytic components are given in the teachings of US. Pat. No. 3,108,081 for these phthalocyanine catalysts.

Although this treatment step can be performed according to any of the methods taught in the art for contacting a liquid stream and a gas stream with a solid catalyst, the preferred system involves a fixed bed of the solid oxidizing catalyst disposed in a treatment zone. The aqueous waste stream is then passed therethrough in either upward, radial, or downward flow and the oxygen stream is passed thereto in either concurrent or countercurrent fiow relative to the aqueous waste stream. Because one of the products of this treatment step is elemental sulfur, there is a substantial catalyst contamination problem caused by the deposition of this elemental sulfur on the fixed bed of the catalyst. In general, in order to avoid sulfur deposition on the catalyst, We prefer to operate this step in either of two alternative modes. In the first mode, a sulfur solvent is admixed with the waste stream and charged to the treatment zone in order to effect removal of deposited sulfur from the solid catalyst. Any suitable sulfur solvent may be utilized provided that it is substantially inert to the conditions utilized in the treatment zone and that it dissolves substantial quantities of sulfur. Examples of suitable sulfur solvents are: disulfide compounds such as carbon disulfide, methyldisulfide, ethyldisulfide, etc.; aromatic compounds such as benzene, toluene, xylene, ethylbenzene, etc.; aliphatic paraffins such as pentane, hexane, heptane, etc.; cyclic parafiins such as methylcyclopentane, cyclopentanes, cyclohexane, etc.; halide compounds such as carbon tetrachloride, methylene chloride, ethylene chloride, chloroform, tetrachloroethane, butyl chloride, propyl bromide, ethyldibromide, chlorobenzene, dichlorobenzene, etc.; and the like solvents. Moreover, mixtures of these solvents may be utilized if desired, and in particular a solvent which is particularly effective is an aromatic-rich reformate. In this mode, the preferred operation encompasses the utilization of a sulfur solvent that is substantially immiscible with the aqueous waste stream. Furthermore, the solubility of sulfur in the solvent is preferably such that it is markedly greater at a temperature in the range of about 175 F. to about 400 F. than it is in temperatures in the range of about 32 F. to about F. This last preference facilitates removal of sulfur through crystallization if such is desired. Considering all of these requirements, one preferred sulfur solvent is selected from the group consisting of benzene, toluene, xylene, and mixtures thereof. Another group of preferred sulfur soivents are the halogenated hydrocarbons.

The amount of sulfur solvent utilized in this treatment step is a function of the net sulfur production for the particular waste stream, the activity and selectivity characteristics of the catalyst selected, and the solubility characteristics of the sulfur solvent. In general, the volumetric ratio of sulfur solvent to aqueous waste stream is selected such that there is at least enough sulfur solvent to carry away the net sulfur production from the oxidation reaction. As a practical matter, it is convenient to operate at a volumetric ratio substantially in excess of the minimum amount required to strip the sulfur from the catalyst; for example, for aqueous waste streams containing about 3 wt. percent ammonium hydrosulfide a volumetric ratio of about 1 volume of sulfur solvent per volume of waste stream gives excellent results. The exact selection of the volumetric ratio for the particular waste stream and catalyst utilized can be made by a suitable experiment or series of experiments, the details of which would be self-evident to one skilled in the art.

Accordingly, in the first mode of operation of the treatment step, a sulfur solvent and oxygen are charged in admixture with the aqueous waste stream to the treatment zone to produce an effiuent stream comprising the sulfur solvent containing dissolved sulfur formed by the oxidation reaction, and water containing NH OH,

passed to a suitable sulfur recovery zone wherein at least a portion of the dissolved sulfur is removed therefrom by any of the methods known in the art such as crystallization, distillation, etc. A preferred procedure is to distill otf sulfur solvent with recovery of liquid sulfur from the bottoms of the sulfur recovery zone. The lean sulfur solvent recovered frorn this sulfur separation step can then be recycled to the treatment step. It is, of course, understood that it is not necessary to treat all of the sulfur solvent to remove sulfur therefrom; that it is only necessary to treat an amount of the rich sulfur solvent sufficient to recover the net sulfur production. In any event, an aqueous phase containing NH OH and (NH S O* is withdrawn from this separating zone, and passed to a stripping zone wherein at least a portion of the ammonia contained therein is removed to produce an aqueous stream containing (NH S O It is to be noted that in some cases, it is advantageous to allow a relatively high concentration of NH OH to remain in this last stream as the presence of NH OH therein facilitates removal of additional amounts of H 8 in the water-contacting step of the hydrocarbon conversion process. In accordance with the present invention, this last stream is passed to a reduction step, hereinafter described, in order to reduce the minor amount of ammonium thiosulfate contained therein to ammonium polysulfide.

The second mode of operation of the treatment step comprises carefully regulating the amount of oxygen injected in to the treatment zone so that oxygen is provided in an amount less than the stoichiometric amount required to oxidize all of the ammonium hydrosulfide in the aqueous waste stream to elemental sulfur. Hence, for this mode it is required that oxygen be present in a mole ratio less than 0.50 mole of per mole of NH HS and preferably about 0.25 to about 0.45 mole of oxygen per mole of ammonium hydrosulfide in the aqueous waste stream. The exact value within this range is selected such that sufiicient sulfide remains available to react with the net sulfur production-that is to say, this mode of operation requires that sufficient excess sulfide be available to form polysulfide with the elemental sulfur which is the product of the primary oxidation reaction. Since one mole of sulfide will react with many moles of sulfur (i.e. about moles of sulfur per mole of sulfide), it is generally only necessary that a small amount of sulfide remain unoxidized.

In this second mode, an aqueous efiluent stream con taining ammonium polysulfide, (NH S O NH OH and a minor amount of other oxides of sulfur is withdrawn from the treatment step and passed to a polysulfide decomposition zone wherein the polysulfide compound is decomposed to yield an overhead stream containing NH H 8, and H 0 and an aqueous bottom stream containing elemental sulfur, (NH S O and typically some The preferred method for decomposing the polysulfide solution involves subjecting it to conditions, including a temperature in the range of about 100 F. to about 350 F. sufiicent to form an overhead stream containing NH H 5, and H 0 and a bottoms stream comprising elemental sulfur in admixture with an aqueous stream containing (NH S O In most cases, it is advantageous to accelerate the polysulfide decomposition reaction by stripping H 8 from the polysulfide solution with the aid of a suitable inert gas such as steam, air, fiue gas, etc., which can be injected into the bottom of the decomposition zone. When this bottom stream contains a slurry of sulfur, it is then subjected to any of the techniques taught in the art for removing a solid from a liquid such as filtration, settling, centrifuging, etc. to remove the elemental sulfur therefrom. In some cases, this bottom stream will contain molten sulfur which can be separated by a suitable settling step. The resulting aqueous stream separated from the sulfur contains a minor amount of (NH S O and in accordance with the present invention is subjected to the reduction step as is hereinafter described. As noted above, it is advantageous to allow some NH OH to remain in this last stream. In the case where the bottom temperature of the decomposition zone is maintained about 250 F., the separation of elemental sulfur from the aqueous recycle stream can be performed, if desired, within the decomposition zone by allowing a liquid sulfur phase to form at the bottom of this zone, and separately drawing off the aqueous stream and a liquid sulfur stream.

An essential reactant for both modes of the treatment step is oxygen. This may be present in any suitable form either by itself or mixed with other inert gases. In general, it is preferred to utilize air to supply the necessary oxygen. As indicated hereinbefore in the second mole, the amount of oxygen utilized is less than the stoichiometric amount required to oixidize all of the ammonium hydrosulfide to elemental sulfur, and in the first mode of operation, wherein a sulfur solvent is utilized, the amount of oxygen is ordinarily chosen to be slightly greater than the stoichiometric amount necessary to oxidize all sulfide to sulfur; that is, oxygen is generally utilized in the first mode in a mole ratio of about 0.5 :1 to about 1.5 :1 or more moles of oxygen per mole of ammoniumhydrosulfide contained in the aqueous waste stream.

Regarding the conditions utilized in the treatment step of the present invention, it is preferred for both preferred modes of operation to utilize a temperature in the range of about 30 F. up to about 400 F. with a temperature of about F. to about 220 F. yielding best results. In fact, it is especially preferred to operate with a temperature less than 200 F., since this minimizes sulfate formation. The sulfide oxidation reaction is not too sensitive to pressure and, accordingly, any pressure which maintams the waste stream in the liquid phase may be utilized. In general, it is preferred to operate at superatmospheric pressure in order to facilitate contact between the oxygen and the waste stream, and pressures of about 25 p. s.1.g. to about 75 p.s.i.g. are particularly preferred. Addrtionally the liquid hourly space velocity (defined to be the volume rate per hour of charging the aqueous waste stream divided by the total volume of the treatment zone containing catalyst) is preferably selected from the range of about 0.5 to about 10.0 hrr Regardless of which mode of operation is utilized in the treatment step, an aqueous stream containing is ultimately recovered therefrom. In accordance with the present invention, this stream is subjected to a reduction step with a sulfide-containing stream, which typically is a gas stream containing H S or a liquid stream containing (NH S or NH HS, and the resulting effiuent stream from the reduction step is passed to the hydrocarbon conversion step. Any suitable sulfide-containing stream can be utilized in this reduction step; however, it is preferred to derive this stream from one or more of the following sources. One preferred source is a drag stream from the aqueous waste stream Withdrawn from the high pressure separating zone utilized in the hydrocarbon conversion process. A second preferred source is the overhead stream containing NH H S, and H which is recovered from the polysulfide decomposition zone when the treatment step is operated in the polysulfide mode. Another preferred source of a suitable sulfide-containing stream is a portion of the H S-rich flash gas typically produced when the hydrocarbon-rich liquid product stream recovered from the eflluent from the hydrocarbon conversion step is passed to a low pressure separating zone wherein a H S-rich gas is flashed off typically at a pressure of about 75 p.s.i.g. and a temperature of about 100 F.

Irrespective of the source of the sulfide-containing stream, it is necessary to provide suflicient sulfide to reduce the thiosulfate to elemental sulfur and to react with the resulting sulfur to produce a polysulfide. We have found good results when the mole ratio of sulfide to thiosulfate is selected from the range of about 2:1 to about :1 or more, with a value of about 2:1 to about 4: 1 being preferred.

This reduction step is conducted at the following conditions: a temperature of about 200 F. to about 700 F. and preferably about 325 F. to about 400 F.; a pressure which is generally suflicient to maintain a part of the water in the liquid phase, and preferably a pressure of about 100 to 5000 p.s.i.g.; and a contact time of about 0.01 to about 2 hours, and preferably about 0.05 to about 0.2 hour. It is to be noted that the reduction step does not require a catalyst. Moreover, the input streams may be passed to this step in either countercurrent or concurrent flow with the latter being preferred.

An aqueous efiluent stream containing ammonium polysulfide is withdrawn from this reduction step; and, in accordance with the present invention, is charged to a polysulfide decomposition step in order to decompose the polysulfide to produce an overhead stream containing NH H 5, and H 0 and an aqueous bottom stream containing elemental sulfur. Thereafter, sulfur is sepa rated from the bottom stream from the polysulfide decomposition step to form a substantial thiosulfide-free and elemental sulfur-free aqueous recycle stream. Both the polysulfide decomposition step and the sulfur separation are preferably operated in the manner previously disclosed.

The resulting aqueous recycle stream is then recycled directly to the water-contacting step of the hydrocarbon conversion process in order to provide the water needed for keeping the elfluent condenser free of sulfide salts, and to avoid contamination of the hydrocarbon product stream with elemental sulfur.

Having broadly characterized the essential steps comprising the method of the present invention, reference is now had to the attached drawing for a detailed explanation of an example of a preferred flow scheme employed therewith. The attached drawing is merely intended as a general representation of the flow scheme employed with no intent to give details about heaters, condensers, pumps, compressors, valves, process control equipment, etc. except where a knowledge of these devices is essential to an understanding of the present invention or would not be self-evident to one skilled in the art. In addition, in order to provide a working example of a preferred mode of the present invention, the attached drawing is discussed with reference to a particularly preferred mode of operation of each of the steps of the present invention and preferred catalyst for use in these steps.

Referring now to the attached drawing, a light gas oil is commingled with a cycle stock at the junction of line 11 and line 1, and with a recycle hydrogen stream at the junction of line 7 with line 1. The resulting mixture is then heated via a suitable heating means (not shown) to the desired conversion temperature and then passed into hydrocarbon conversion zone 2. An anaylsis of the light gas oil shows it to have the following properties; and API gravity at 60 F. of 25, an initial boiling point of 421 F., a 50% boiling point of 518 F., and an end boiling point of 663 F., a sulfur content of 2.21 wt. percent, and a nitrogen content of 126 wt. p.p.m. Hydrogen is supplied via line 7 at a rate corresponding to a hydrogen recycle ratio of 10,000 standard cubic feed to hydrogen per barrel of oil charged to hydrocarbon conversion zone 2. The cycle stock which is being recycled via line 11 is a portion of the 400+ fraction of the product stream which is separated in product recovery system 10 as will be hereinafter explained. The catalyst utilized in zone 2 comprises nickel sulfide combined with a carrier material containing silica and alumina in a weight ratio of about 3 parts silica per part of alumina. The nickel sulfide is present in amounts suflicient to provide about 5.0 wt. percent nickel in the final catalyst. The catalyst is maintained within zone 2 as a fixed bed of /8 inch by /3 inch cylindrical pills. The conditions utilized in zone 2 are hydrocracking conditions which include a pressure of about 1500 p.s.i.g., and conversion temperature of about 600 F., and a liquid hourly space velocity of about 2.0 hr. based on combined feed. An eflluent stream is then withdrawn from zone 2, via line 3 commingled with a water stream at the junction of line 9 with line 3 and the resulting mixture passed into cooling means 4 wherein it is cooled to a temperature of about F. The cooled mixture is then passed via line 5 into separating zone 6 which is maintained at a temperature of about 100 F. and a pressure of about 1450 p.s.i.g. The amount of water injected into line 3 via line 9 is about 5 gallons of water per 100 gallons of oil. As explained hereinbefore, the reason for adding the water on the influent side of condenser 4 is to insure that this condenser does not become clogged with sulfide salts.

In separating zone 6, a three-phase system is formed. The gaseous phase comprises hydrogen, hydrogen sulfide and a minor amount of light ends. The oil phase contains a relatively large amount of dissolved H S. The water phase contains about 5 wt. percent ammonium hydrosulfide with a slight molar excess of ammonia. The hydrogenrich gaseous phase is withdrawn via line 7 and a portion of it, (about 20 vol. percent) is vented from the system via line 13 in order to prevent build-up of excessive amounts of H S in this stream. The remainder of the hydrogen stream is passed via line 7 through compressive means, not shown, and is commingled with additional make-up hydrogen entering the process via line 30 and passed back to hydrocarbon conversion zone 2. The oil phase from separating zone 6 is withdrawn via line 8 and passed to product recovery system 10.

In this case, product recovery system 10 comprises a low pressure separating zone and a suitable train of fractioning means. In the low pressure separating zone, the product stream is maintained at a pressure of about 100 p.s.i.g. and a temperature of about 100 F. in order to flash off dissolved H S from this oil stream. The resulting stripped oil stream is fractionated to recover a gasoline boiling range product stream and a cycle oil comprising the portion of the product stream boiling above 400 F. The gasoline product stream is recovered via line 12 and the cycle oil is recycled to hydrocarbon conversion zone 2 via line 11.

Returning to the aqueous phase formed in separating zone 6, it is withdrawn via line 9 and continuously recycled back to line 3. Additional make-up water is injected through line 14 during start-up of the process and to make up for losses during the course of the process. It is a feature of the present invention that the requirement for make-up water is minimized. Two drag streams are withdrawn from the water stream flowing through line 9, the first at the junction of line 23 with line 9, and the second at the junction of line 15 with line 9. This second drag stream is passed via line 15 to line 16 where it is commingled with an air stream, and the resulting mixture is passed into treatment zone 17.

Treatment zone 17 contains a fixed bed of a solid catalyst comprising cobalt phthalocyanine mono-sulfonate 13 combined with an activated carbon carrier material in an amount such that the catalyst contains 0.5 wt. percent phthalocyanine catalyst. The activated carbon granules used as the carrier material are in a size of 30-4 mesh. Ammonium hydrosulfide is present in the aqueous stream in an amount of about wt. percent and this stream is charged to treatment zone 17 at a liquid hourly space velocity of about 1.0 hr. -1. The amount of air which is also charged to treatment zone 17 .via line 16 is sufficient to provide about 0.7 atom of oxygen per atom of sulfide contained in the waste water stream. As previously explained, this is an amount less than the stoichiometric amount necessary to convert the sulfide to sulfur, and consequently ammonium polysulfide is formed with treatment zone 17. The conditions utilized in this zone are a temperature of 95 F. and a pressure of 50 p.s.i.g. Because of side reactions, a minor amount of the sulfide contained in the aqueous waste stream is oxidized to higher oxides of sulfur, principally (NH S O Depending somewhat upon the life of the catalyst utilized within zone 17, about 1 to about or more of the sulfide will be oxidized to (NH S O Accordingly, the effluent stream withdrawn from zone 17 via line 18 contains ammonium polysulfide, NH OH, (NH S O and a minor amount of nitrogen gas. This stream is passed to the first separating system, 19, which in this case comprises: a gas separator, a first polysulfide decomposition zone and a first sulfur recovery zone. In the gas separator, the minor amount of nitrogen gas contained in the effluent stream from treatment zone 17 is vented from the system. In the first polysulfide decomposition zone, the liquid efiluent stream from the gas separator is heated to a temperature of about 210 F. and passed into a distillation column wherein an overhead stream containing NH H 0, and a minor amount of H 8 is recovered via line 20 and a bottom stream containing a slurry of elemental sulfur in an aqueous solution of (NH S O is withdrawn as a bottom stream. This bottom stream is passed to a first sulfur recovery Zone wherein the elemental sulfur is filtered from this stream and recovered via line 22. The resulting elemental sulfur-free aqueous stream containing a minor amount of (NH S O is Withdrawn from separating system 19 via line 21 and commingled with the first drag stream, which was withdrawn from the aqueous waste stream from separating zone 6, at the junction of line 23 with line 21. As previously mentioned, NH HS is present in the aqueous waste stream flowing through line 23 in an amount of about 5 wt. percent, and a sufficient amount of this stream is commingled with the stream flowing through line 21 to provide a mixture containing a mole ratio of sulfide to thiosulfate of about 3:1. The resulting mixture is passed through suitable heating means into reduction zone 24 which is maintained at a temperature of 375 F., and a pressure of 250 p.s.i.g. The contact time is about 5 minutes. An analysis of the effluent from zone 24 indicates that about 70 wt. percent of the ammonium thiosulfate is converted to ammonium polysulfide. The resulting aqueous stream containing ammonium polysulfied is withdrawn from zone 24 via line 25 and passed to the second separating system, 26, which in this case comprises: a second polysulfide decomposition zone and a second sulfur recovery zone. In the second polysulfide decomposition zone, the aqueous stream from line 26 is maintained at a temperature of about 280 F. and a pressure of about 40 p.s.i.g. which are effective to decompose the polysul tide and produce a second overhead stream containing NH H 8 and H 0, which is recovered via line 27, and a bottoms stream containing a mixture of liquid sulfur and a treated aqueous stream. In this case, because the sulfur is in liquid form, the lower portion of the decomposition zone is utilized as the second sulfur separating zone and the liquid sulfur is allowed to form a separate bottom phase which is drawn ofi via line 28. The aqueous phase that separates from the liquid sulfur phase is withdrawn via line 29 and found to be substantially free of both ammonium polysulfide and elemental sulfur. Thereafter, it is recycled via line 29 and line 9 to the water-contacting step of the hydrocracking process: that is to the junction of line 9 with line 3.

Operations as indicated are continued for a hydrocracking catalyst life of about 20 barrels per pound of catalyst and the product stream recovered via line 12 remains substantially free of elemental sulfur and there are no significant aqueous waste stream disposal problems. Therefore, a waste water disposal pollution problem has been abated, elemental sulfur has been recovered from the waste stream, and the loop is closed with respect to recycle water.

We claim as our invention:

1. A method for treating an aqueous waste stream containing NH HS which comprises (a) catalytically treating the aqueous waste stream with oxygen at oxidizing conditions effective to produce an effluent stream containing NH OH, (NH S O and elemental sulfur or ammonium polysulfide;

(b) separating sulfur and ammonia from the effluent stream from step (a) to form an aqueous stream containing (NH S O (c) admixing the aqueous stream from step (b) with a sulfide-containing stream and subjecting the mixture to reduction conditions effective to produce an effluent stream containing a minor amount of ammonium polysulfide;

(d) subjecting the efiluent stream from step (c) to polysulfide decomposition conditions effective to produce an overhead stream containing NH H 8, and H 0 and an aqueous bottom stream containing elemental sulfur; and

(e) separating sulfur from the bottom stream produced in step (d) to form a substantially thiosulfate-free and elemental sulfur-free aqueous stream.

2. The method as defined in claim 1 wherein step (a) comprises contacting the aqueous Waste stream and oxygen with a phthalocyanine catalyst at oxidizing conditions effective to produce an efiluent stream containing NH OH, (NH S O and elemental sulfur or ammonium polysulfide.

3. The method as defined in claim 1 wherein step (a) comprises contacting said aqueous waste stream and oxygen with a catalyst comprising an iron group metallic sulfide combined with a carrier material at oxidizing conditions effective to produce an effluent stream containing NH OH, (NH S O and elemental sulfur or ammonium polysulfide.

4. The method as defined in claim 1 wherein the reduction conditions utilized in step (c) include a temperature of about 200 to about 700 F., a pressure sufiicient to maintain a part of the aqueous stream in the liquid phase, and a contact time of about 0.01 to about 2 hr.

5. The method as defined in claim 1 wherein a waterimmiscible sulfur solvent is also charged to step (a) and wherein step (b) comprises: separating the eflluent stream from step (a) into a sulfur solvent phase containing sulfur and an aqueous phase containing NH OH and (NH S O and stripping at least a portion of the ammonia from this aqueous phase to produce an aqueous stream containing (NH S O 6. The method as defined in claim 1 wherein step (a) is operated at a mole ratio of O to NH HS not greater than 0.5 :1 to produce an aqueous effluent stream containing ammonium polysulfide, NH OH, and (NH S O and wherein step (b) comprises: subjecting the effluent stream from step (a) to polysulfide decomposition conditions effective to produce an overhead stream containing NH H S, and H 0 and aqueous bottom stream containing elemental sulfur and (NH S O and separating sulfur from the bottom stream to produce an aqueous stream containing (NH S O 7. The method as defined in claim 1 wherein the sulfide containing stream utilized in step (c) is a portion of the aqueous waste stream containing NH HS.

8. The method as defined in claim 6 wherein the sulfidecontaining stream utilized in step (c) is at least a portion of the overhead stream containing NH H 0, and H resulting from the decomposition of the ammonia polysulfide in step (b).

9. The method as defined in claim 1 wherein the sulfidecontaining stream utilized in step (c) is an H S-rich gas stream.

10. A method for treating an aqueous waste stream containing NH HS which comprises (a) contacting a first portion of the aqueous waste stream and oxygen in an amount such that the mole ratio of oxygen to NH HS is less than 0.5 :1, with phthalocyanine catalyst at oxidizing conditions suflicient to produce an aqueous efiluent stream containing ammonium polysulfide, NH OH, and

(b) subjecting the aqueous effluent stream produced in step (a) to polysulfide decomposition conditions effective to produce a first overhead stream containing NH H S, and H 0, and an aqueous bottom stream containing elemental sulfur and (NH S O (c) separating sulfur from the bottom stream produced in step (b) to form an aqueous stream containing 02 2 3;

(d) admixing the aqueous stream formed in step (c) with a second portion of the aqueous waste stream and subjecting the mixture to reduction conditions effective to produce an aqueous efiluent stream containing a minor amount of ammonium polysulfide;

(e) subjecting the efiiuent stream from step (d) to polysulfide decomposition conditions effective to produce a second overhead stream containing NH H 8, and H 0, and an aqueous bottom stream containing elemental sulfur; and

(f) separating sulfur from the bottom stream produced in step (e) to form an aqueous stream which is substantially free of both ammonium thiosulfate and elemental sulfur.

11. The method as defined in claim 10 wherein the reduction conditions utilized in step (d) include a temperature of about 325 to about 400 F., a pressure of about to about 5,000 p.s.i.g., and a contact time of about 0.05 to about 0.2 hour.

12. The method as defined in claim 10 wherein the mole ratio of sulfide to thiosulfate utilized in step (d) is about 2:1 to about 4:1.

References Cited UNITED STATES PATENTS 3,340,182 9/1967 Berkman et a1. 208--212 3,029,201 4/1962 Brown et a1 21063 X 3,460,913 8/1969 Hoekstra 23-224 MICHAEL E. ROGERS, Primary Examiner US. Cl. X.R. 

